Electron beams are now in widespread use in the radiation treatment of cancer because their rapid dose falloff minimizes irradiation of critical healthy tissues beyond the treatment volume. Unfortunately, for treatment planning purposes it is not yet possible to routinely calculate the absorbed dose distribution accurately, particularly in the presence of tissue inhomogeneities and body curvature. The overall goal of the proposed research is to develop electron dose-calculation algorithms which are sufficiently accurate for the most complicated situations expected to be encountered clinically, yet practical in the sense of being able to be implemented in a computerized treatment planning system (short enough calculation time). Our goal is to achieve in these computer algorithms an accuracy of 5%, or preferably 3%, throughout the treatment volume. During these final four years of the research, theoretical models already developed from the basic laws of physics will be mathematically simplified for implementation as computer algorithms. Several theoretical models for certain physical processes, still required, will also be developed at this time. EGS4 Monte Carlo calculations, to check the accuracy of the theoretical models and their attendant algorithms, will continually be carried out. The developing set of computer algorithms, using CT-Scan data directly as input, will be experimentally verified for accuracy through a consulting relationship with a university radiotherapy department. This comparison between the predictions of the algorithms and experimental results, starting with relatively simple configurations of inhomogeneities and progressing to use of a complex anthropomorphic phantom, will be carried out throughout the four years of the project.